Direct injection fuel systems may be used to deliver at least a portion of a desired amount of fuel to an engine for combustion. Such direct injection fuel systems may include a high pressure fuel pump, in addition to a low pressure fuel pump, upstream of a fuel rail to raise a pressure of the fuel delivered to the engine cylinders through the direct injectors. In vehicle start/stop systems configured to perform an idle-stop when idle-stop conditions are met and automatically restart the engine when restart conditions are met, the high pressure pump may also be used to compression inject fuel into one or more cylinders and restart the engine. In particular, during engine restart conditions, the high pressure pump may be used to provide sufficient injector pressure to force fuel into the selected cylinders during a compression stroke, thereby reducing engine restart times as well as restart engine speed flares.
However, the inventors herein have identified potential issues with such systems. As one example, during conditions when the high pressure fuel pump is degraded, the fuel rail pressure may be reduced to a lower level corresponding at least to the low pressure fuel pump. If the high pressure pump is degraded at the time of engine restart, the reduced pressure level may not be sufficient to force the fuel into the cylinder during the compression stroke. As a result, no combustion may occur during cranking and the starter may fault. If the high pressure pump degrades during the run up (e.g., after the first or second combustion event during the run up), an engine stall may occur. Engine misfire events may also be possible. As such, the overall engine restart response may be degraded. The effects may be exacerbated in vehicle start/stop systems due to the higher frequency of engine restarts from idle-stop conditions.
Thus at least some of the above issues may be addressed by a method of operating an engine comprising, during an engine cold start condition, direct injecting fuel into a first firing cylinder during an intake stroke independent of a state of a high pressure fuel pump coupled to the engine to restart the engine. In this way, engine startability can be improved even if the high pressure fuel pump is degraded.
In one example, during an engine restart, it may be determined if a high pressure fuel pump is degraded. If so, fuel may be injected into the first firing cylinder (e.g., the first cylinder to reach TDC after the engine starts to rotate) during the intake stroke. For example, the fuel injection may be shifted from multiple injections in the compression stroke to a single injection in the intake stroke. Optionally, direct fuel injection during the intake stroke may be maintained for a number of combustion events since the engine start. In one example, the intake stroke injection may be maintained until a threshold engine speed is reached (e.g., until an idling speed is reached). While direct injecting during the intake stroke, a spark timing may be retarded. However, a lower amount of spark retard may be applied for the intake stroke injection relative to a corresponding compression stroke injection, to reduce the engine speed flare while providing combustion torque. Likewise, while direct injecting during the intake stroke, a smaller alternator load may be applied on the engine relative to the corresponding compression stroke injection, to reduce restart NVH issues and improve vehicle launch smoothness. Still other throttle, valve timing, transmission gear, etc. adjustments may be performed in coordination with the intake stroke injection to improve engine restart in the presence of a degraded high pressure fuel pump.
In this way, by injecting fuel in the intake stroke during an engine restart, in response to an indication of high pressure pump failure, sufficient injector pressure may be developed to force fuel into the first firing cylinder. As such, this improves engine restartability and reduces the likelihood of engine stalls and misfires. By adjusting one or more engine parameters while injecting the fuel during an intake stroke, engine speed flares and NVH issues associated with an engine restart can also be addressed. Overall, an engine may be restarted even if a high pressure pump is degraded.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.